Seismic activity increases at Iceland volcano

FILE- A plume of ash, dust and steam emits from a volcano erupting beneath Iceland's Eyjafjallajokull glacier, in this file photo dated Wednesday, April 21, 2010, in Eyjafjallajokull, Iceland. A surge of small earthquakes has been reported Tuesday Sept. 6, 2011, around Iceland's Katla volcano, but scientists said Tuesday there is no immediate concern that the increased seismic activity will trigger a dangerous eruption, although history has shown that when the Eyjafjallajokull volcano erupts, Katla isn't far behind. (AP Photo/Carolyn Kaster, File)
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FILE- A plume of ash, dust and steam emits from a volcano erupting beneath Iceland's Eyjafjallajokull glacier, in this file photo dated Wednesday, April 21, 2010, in Eyjafjallajokull, Iceland. A surge of small earthquakes has been reported Tuesday Sept. 6, 2011, around Iceland's Katla volcano, but scientists said Tuesday there is no immediate concern that the increased seismic activity will trigger a dangerous eruption, although history has shown that when the Eyjafjallajokull volcano erupts, Katla isn't far behind. (AP Photo/Carolyn Kaster, File)
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REYKJAVIK, Iceland 
A surge of small earthquakes has been reported around Iceland's Katla volcano, but scientists said Tuesday there is no immediate concern that the increased seismic activity will trigger a dangerous eruption.

Although earthquakes around Katla are common, an increase in cluster earthquakes is not.

"It's one of the most feared volcanos, so we're closely monitoring it," said Pall Einarsson of the University of Iceland. "That said, it's normal for earthquakes to be detected around Katla. What's a bit unusual is that we're seeing swarms of small earthquakes, some occurring every 10 minutes or so."

After flying over the area to monitor the situation Tuesday evening, scientists said they could not yet determine what caused the increased seismic activity. Although they detected signs that Katla was preparing for an eruption, they also emphasized that the volcano had also seen similar activity without erupting before.

Nevertheless, "there are signs of Katla being more active now than in the past few years so there is every reason to keep an eye on her," said Magnus Tumi Gudmundsson, a professor of geophysics at the University of Iceland, after the flight.

Iceland sits on a large volcanic hot spot in the Atlantic's mid-oceanic ridge. Eruptions, common throughout Iceland's history, are often triggered by seismic activity when the Earth's plates move and when magma from deep underground pushes its way to the surface.

Like earthquakes, predicting the timing of volcanic eruptions is an imprecise science.

Last year's eruption of the Eyjafjallajokull volcano forced hundreds of people to be evacuated and paralyzed international air travel for weeks because of a hovering ash cloud.

And history has shown that when the Eyjafjallajokull volcano erupts, Katla - located under the massive Myrdalsjokull icecap - isn't far behind.

Katla, which threatens disastrous flooding if its ice cap melts, typically awakens every 80 years or so, and last erupted in 1918.

Activity around Katla started to increase around July but has since grown even stronger. The strongest earthquake detected so far has been a 3.0 magnitude. There also was flooding that wiped out a bridge in July.

Like people, each volcano has a different personality of sorts, says Einarsson.

"We look at the behavior, try to analyze patterns and then try to come up with an explanation," says Einarsson. "This is a bit difficult to interpret so far, but it's correct to say that it signals some sort of activity in the volcano and some sort of magna intrusions are probably taking place."

Geologists also are worried about the Hekla volcano, which unlike Katla, is not covered by a glacier and produces little seismic activity.

During the Middle Ages, Icelanders called the Hekla volcano, the country's most active, the "Gateway to Hell," believing that souls were dragged into the fire below.

"If we saw earthquakes like this in Hekla, we would immediately signal a warning sign," Einarsson said.

Another one of Iceland's volcanos proved particularly deadly in 1783.

When Laki erupted, it freed gases that turned into smog. The smog floated across the jet stream, changing weather patterns. Many died from gas poisoning in the British Isles. Crop production fell in western Europe. Famine spread.

"Everyone has their eyes on a big Katla eruption," said Andy Russell with Newcastle University's Earth Surface Processes Research Group, who travels frequently to Iceland for research. "You can never say never, but I don't think there's need for alarm right now."

Russell said past Katla eruptions have caused floods the size of the Amazon and sent boulders as big as houses tumbling down valleys and roads. Flooding occurred within 45 minutes of the eruption, he said.

Iceland is one of the few places in the world where a mid-ocean ridge actually rises above sea level. Many volcanic eruptions along the ocean basin often go undetected because they can't be easily seen.